Electronic device containing carbon nanotubes

ABSTRACT

An electronic device including a pair of electrodes disposed on a substrate and carbon nanotubes electrically connecting the electrodes. A method for manufacturing this device in which the electrodes are disposed on the substrate and the nanotubes are prepared to electrically connect the electrodes.

This application is a continuation of application Ser. No. 11/556,254,filed Nov. 3, 2006, which is a division of application Ser. No.11/250,454, filed Oct. 17, 2005, now U.S. Pat. No. 7,148,619, which is adivision of application Ser. No. 10/712,101, filed Nov. 14, 2003, nowU.S. Pat. No. 6,979,244, which is a division of U.S. application Ser.No. 10/435,536, filed May 12, 2003, now U.S. Pat. No. 6,720,728, whichis a division of U.S. application Ser. No. 09/178,680, filed Oct. 26,1998, now U.S. Pat. No. 6,628,053. All prior applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a carbon nanotube device using a carbonnanotube and a manufacturing method thereof. More particularly, theinvention relates to a carbon nanotube device applicable to a functionaldevice such as a quantum-effect device, an electronic device, amicro-machine device or a bio-device etc. Further, the invention relatesto a carbon nanotube device applicable to an electron source, an STM(scanning type tunnel microscope) probe, or an ATM (atomic forcemicroscope) probe by the utilization of sharpness of the carbonnanotube, and a manufacturing method thereof.

The invention relates also to an electron emitting device for a display,a cathode ray tube, an emitter, a lamp or an electronic gun.

2. Description of the Related Art

Fibrous carbon is generally called carbon fiber, and for carbon fiberthat is used as a structural material having a diameter of at leastseveral μm, several manufacturing methods have been studied. Among thosestudied, a method for manufacturing the carbon fiber from a PAN(polyacrylonitrile)-based fiber or a pitch-based fiber is considered tobe a mainstream method.

Schematically, this method comprises making a raw material spun from aPAN fiber, an isotropic pitch or a meso-phase pitch non-meltable andhardly flammable, carbonizing the resultant material at a temperaturewithin a range of from 800 to 1,400° C., and treating the resultantproduct at a high temperature within a range of from 1,500 to 3,000° C.The carbon fiber thus obtained is excellent in mechanical propertiessuch as strength and modulus of elasticity, and for its light weightthat can be used for a sporting good, an adiabatic material and astructural material for space or automotive purposes in the form of acomposite material.

On the other hand, a carbon nanotube has recently been discovered havinga tubular structure whose diameter is 1 μm or less. An ideal structureof the carbon nanotube is a tube formed with a sheet of carbon hexagonalmeshes arranged in parallel with its tube axis. A plurality of suchtubes forms a nanotube. The carbon nanotube is expected to havecharacteristics like metals or semiconductors, depending upon bothdiameter of the carbon nanotube and the bonding form of the carbonhexagonal mesh sheet. Therefore, the carbon nanotube is expected to be afunctional material in the future.

Generally, carbon nanotubes are synthesized by the application of thearc discharge process, a laser evaporation process, a pyrolysis processand the use of plasma.

(Carbon Nanotube)

An outline of a recently developed carbon nanotube will now bedescribed.

A material having a diameter of up to 1 μm, smaller than that of carbonfiber, is popularly known as a carbon nanotube to discriminate fromcarbon fiber, although there is no definite boundary between them. In anarrower sense of the words, a material having the carbon hexagonal meshsheet of carbon substantially in parallel with the axis is called acarbon nanotube, and one with amorphous carbon surrounding a carbonnanotube is also included within the category of carbon nanotube.

The carbon nanotube in the narrower definition is further classifiedinto one with a single hexagonal mesh tube called a single-wallednanotube (abbreviated as “SWNT”), and one comprising a tube of aplurality of layers of hexagonal meshes called a multiwalled nanotube(abbreviated as “MWNT”).

Which of these types of carbon nanotube structures is available isdetermined to some extent by the method of synthesis and otherconditions. It is however not as yet possible to produce carbonnanotubes of the same structure.

These structures of a carbon nanotube are briefly illustrated in FIGS.1A to 4B. FIGS. 1A, 2A, 3A and 4A are schematic longitudinal sectionalviews of a carbon nanotube and carbon fiber, and FIGS. 1B, 2B, 3B and 4Bare schematic sectional views illustrating transverse sections thereof.

The carbon fiber has a shape as shown in FIGS. 1A and 1B in which thediameter is large and a cylindrical mesh structure in parallel with itsaxis has not grown. In the gas-phase pyrolysis method using a catalyst,a tubular mesh structure is observed in parallel with the axis near thetube center as shown in FIGS. 2A and 2B, with carbon of irregularstructures adhering to the surrounding portions in many cases.

Application of the arc discharge process or the like gives an MWNT inwhich a tubular mesh structure in parallel with its axis grows at thecenter as shown in FIGS. 3A and 3B, with a slight amount of amorphouscarbon adhering to surrounding portions. The arc discharge process andthe laser deposition process tend to give an SWNT in which a tubularmesh structure grows as shown in FIGS. 4A and 4B.

The following three processes are now popularly used for the manufactureof the aforementioned carbon nanotube: a process similar to thegas-phase growth process for carbon fiber, the arc discharge process andthe laser evaporation process. Apart from these three processes, theplasma synthesizing process and the solid-phase reaction process areknown.

These three representative processes will now be described:

(1) Pyrolysis Process Using Catalyst

This process is substantially identical with the carbon fiber gas-phasegrowth process. The process is described in C. E. Snyders et al.,International Patent No. W089/07163 (International Publication Number).The disclosed process comprises the steps of introducing ethylene orpropane with hydrogen into a reactor, and simultaneously introducingsuper-fine metal particles. Apart from these raw material gases, asaturated hydrocarbon such as methane, ethane, propane, butane, hexane,or cyclohexane, and an unsaturated hydrocarbon such as ethylene,propylene, benzene or toluene, acetone, methanol or carbon monoxide,containing oxygen, may be used as a raw material.

The ratio of the raw material gas to hydrogen should preferably bewithin a range of from 1:20 to 20:1. A catalyst of Fe or a mixture of Feand Mo, Cr, Ce or Mn is recommended, and a process of attaching such acatalyst onto fumed alumina is proposed.

The reactor should preferably be at a temperature within a range of from550 to 850° C. The gas flow rate should preferably be 100 sccm per inchdiameter for hydrogen and about 200 sccm for the raw material gascontaining carbon. A carbon tube is generated in a period of time withina range of from 30 minutes to an hour after introduction of fineparticles.

The resultant carbon tube has a diameter of about 3.5 to 75 nm and alength of from 5 to even 1,000 times as long as the diameter. The carbonmesh structure is in parallel with the tube axis, with a slight amountof pyrolysis carbon adhering to the outside of the tube.

H. Dai et al. (Chemical Physico Letters 260, 1996, p. 471-475) reportthat, although at a low generating efficiency, an SWNT is generated byusing Mo as a catalytic nucleus and carbon monoxide gas as a rawmaterial gas, and causing a reaction at 1,200° C.

(2) Arc Discharge Process

The arc discharge process was first discovered by Iijima, and detailsare described in Nature (vol. 354, 1991, p. 56-58). The arc dischargeprocess is a simple process of carrying out DC arc discharge by the useof carbon rod electrodes in an argon atmosphere at 100 Torr. A carbonnanotube grows with carbon fine particles of 5 to 20 nm on a part of thesurface of the negative electrode. This carbon tube has a diameter offrom 4 to 30 nm and a length of about 1 μm, and has a layered structurein which 2 to 50 tubular carbon meshes are laminated. The carbon meshstructure is spirally formed in parallel with the axis.

The pitch of the spiral differs for each tube and for each layer in thetube, and the inter-layer distance in the case of a multi-layer tube is0.34 nm, which substantially agrees with the inter-layer distance ofgraphite. The leading end of the tube is closed by a carbon network.

T. W. Ebbesen et al. describe conditions for generating carbon nanotubesin a large quantity by the arc discharge process in Nature (vol. 358,1992, p. 220-222). A carbon rod having a diameter of 9 mm is used as acathode and a carbon rod having a diameter of 6 nm, as an anode. Theseelectrodes are provided opposite to each other with a distance of 1 mmin between in a chamber. An arc discharge of about 18 V and 100 A isproduced in a helium atmosphere at about 500 Torr.

At 500 Torr or under, the ratio of the carbon nanotubes is rather low,and at over 500 Torr, the quantity of generation decreases as a whole.At 500 Torr which is the optimum condition, the ratio of carbonnanotubes reaches 75%.

The collection ratio of carbon nanotubes is reduced by causing a changein supplied power or changing the atmosphere to argon one. Morenanotubes are present near the center of the carbon rod.

(3) Laser Evaporation Process

The laser evaporation process was first reported by T. Guo et al. inChemical Physics Letters (243, 1995, p. 49-54), and further, generationof a rope-shaped SWNT by the laser evaporation process is reported by A.Thess et al. in Science (vol. 273, 1996, p. 483-487).

First, a carbon rod formed by dispersing Co or Ni is placed in a quartztube, and after filling the quartz tube with Ar at 500 Torr, the entirecombination is heated to about 1,200° C. Nd-YAG laser is condensed fromthe upstream end of the quartz tube to heat and evaporate the carbonrod. Carbon nanotubes are thus accumulated in the downstream end of thequartz tube. This process is hopeful for selective preparation of SWNTs,and has a feature that SWNTs tend to gather to form a rope shape.

The conventional art will now be described in terms of application ofthe carbon nanotube.

(Application of Carbon Nanotube)

While no applied product of carbon nanotube is available at present,active research efforts are being made for its applications. Typicalexamples of such efforts will be briefly described.

(1) Electron Emission Source

The carbon nanotube, having a shape leading end and being electricallyconductive, is adopted in many research subjects.

W. A. De Heer et al. refined a carbon nanotube obtained by theapplication of the arc discharge process, and placed it upright on asupport via a filter to use it as an electron source (Science, vol. 270,1995, p. 1179). They report that the electron source comprised acollection of carbon nanotubes, and an emission current of at least 100mA was stably obtained by the impression of 700 V from an area of 1 cm².

A. G. Rinzler et al. evaluated properties by attaching an electrode to acarbon nanotube obtained by the arc discharge process, and there wasavailable an emission current of about 1 nA from a carbon nanotube witha closed end, and of about 0.5 μA from a carbon nanotube with an openend, by the impression of about 75 V (Science, vol. 269, 1995, p. 1550).

(2) STM, AFM

H. Dai et al. report, in Nature (384, 1996, p. 147), an application of acarbon nanotube to STM and AFM. According to their report, the carbonnanotube prepared by the arc discharge process was an SWNT having adiameter of about 5 nm at the leading end. Because of a thin tip andflexibility, even the bottom of a gap of a sample could be observed, andthere was available an ideal tip free from a tip crash.

(3) Hydrogen Storing Material

A. C. Dillon et al. report, in Nature (vol. 386, 1997, p. 377-379), thatthe use of an SWNT permits storage of hydrogen molecules of a quantityseveral times as large as that available with a carbon generated from apitch-based raw material. While their study on application has justbegun, it is expected to serve as a hydrogen storing material for ahydrogen car or the like.

In the configuration and manufacturing method of a carbon nanotube inthe conventional art, diameters and directions of resultant carbonnanotubes are very random, and after growth, an electrode is notconnected to the carbon nanotube. More specifically, upon application ofthe carbon nanotube, it is necessary to collect after synthesis forpurifying, and form it into a particular shape in compliance with theshape for application.

For example, when it is to be used as an election source, A. G. Rinzleret al. teaches the necessity to take out a carbon fiber and to bond anend thereof to an electrode, as reported in Science (vol. 269, 1995, p.1550-1553).

Further, as reported in Science (vol. 270, 1995, p. 1179-1180) andScience (vol. 1, 268, 1995, p. 845-847), Walt A. de Heer et al.discloses the necessity to provide a step of purifying a carbon nanotubeprepared by the arc discharge process, and then placing upright thecarbon nanotube on a support by the use of a ceramic filter. In thiscase, an electrode is not positively bonded to the carbon nanotube.Further, the carbon nanotubes in application tend to get entangled witheach other in a complicated manner, and it is difficult to obtaindevices fully utilizing characteristics of the individual carbonnanotubes.

SUMMARY OF THE INVENTION

The present invention was developed in view of the problems as describedabove, and has an object to provide a carbon nanotube device, in which acarbon nanotube has a strong directivity, giving a large quantity ofelectron emission when it is used, for example, as an electron emissiondevice.

Another object of the invention is to provide a manufacturing method ofcarbon nanotube device in which the carbon nanotube binds to aconductive surface so that conduction is maintained therebetween, andthe carbon nanotube has a high directivity.

Further, the invention has an object to provide an electron emissiondevice giving a large quantity of electron emission and having a highperformance.

Specifically, there is provided a carbon nanotube device comprising asupport having a conductive surface and a carbon nanotube, one of whoseterminus binds to said conductive surface at a site so that conductionbetween said conductive surface and said carbon nanotube is maintained,wherein a root of said carbon nanotube where said carbon nanotube bindsto said conductive surface is surrounded by a wall.

Forming the barrier with a layer containing alumina or silicon ispreferable with a view to achieving a higher density of the carbonnanotubes binding to the conductive surface. The wall containing aluminais available, after forming an aluminum thin film on the conductivesurface, for example, by anodically oxidizing aluminum. At this point,the conductive surface should preferably comprises a layer containing atleast one element selected from the group consisting of titanium,zirconium, niobium, tantalum, molybdenum, copper and zinc. It is notnecessary that the conductive surface be previously protected evenduring anodic oxidation of the aluminum thin film.

There is also provided, a manufacturing method of a carbon nanotubedevice comprising a support having a conductive surface and a carbonnanotube, one of whose terminus binds to said conductive surface at asite so that conduction between said conductive surface and said carbonnanotube is maintained, wherein a root of said carbon nanotube at thesite where said carbon nanotube binds to said conductive surface issurrounded by a wall, said method comprising the steps of:

(i) forming a plurality of carbon nanotube binding sites isolated fromeach other by walls on said conductive surface; and

(ii) forming carbon nanotubes at the sites.

Additionally, there is provided an election emitting device comprising:

a carbon nanotube device, which itself comprises a support having aconductive surface and a carbon nanotube, one of whose terminus binds tosaid conductive surface so that conduction between said conductivesurface and said carbon nanotube is maintained, wherein a root of saidcarbon nanotube where said carbon nanotube binds to said conductivesurface is surrounded by a wall;

an electrode located at a position opposite to said conductive surface;and

means for impressing a potential to a space between said conductivesurface and said electrode.

According to the invention as described above, it is possible to controlgrowth direction of the carbon nanotube by means of the wall. As aresult, it is possible to provide an electron emitting device havingexcellent electron emitting properties, and a carbon nanotube devicesuitable for a probe of an STM or an AFM which gives a satisfactoryimage and has a high strength.

In the case where the wall comprises a layer containing alumina orsilicon, it is possible to efficiently form a carbon nanotube devicehaving a configuration in which a plurality of carbon nanotubes bind tothe conductive surface, and binding sites of the individual carbonnanotubes are isolated from each other by the wall. The device of theinvention, provided with carbon nanotubes whose growth directions arealmost the same, and each of which have a uniform directivity isolatedfrom each other at a high density, is suitably applicable for anelectron emitting device or a probe such as an STM or an AFM.

When the conductive surface comprises a layer containing at least onematerial selected from the group consisting of titanium, zirconium,niobium, tantalum, molybdenum, copper and zinc, it is possible to easilyform a carbon nanotube of the invention. More specifically, an aluminathin film having a narrow hole is formed through anodic oxidation alsowhen forming the barrier by anodic oxidation of an aluminum thin film.The anodic oxidation carried out so that the bottom of the narrow holeserves as the electrode surface never damages the conductive surface,and as a result, it is possible to easily form a carbon nanotube bindingconductively to the conductive surface.

In the various features of the present invention as described above, theexpression “a terminus of the carbon nanotube binds conductively to theconductive surface of the support” include, in addition to theembodiment in which the carbon nanotube binds directly to the conductivesurface, an embodiment in which the carbon nanotube is conductivelyconnected to the conductive surface under a tunnel effect via aninsulating layer, and an embodiment in which the carbon nanotube bindsconductively to the conductive surface through an insulating layerincluding a path containing an element composing the conductive surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 4B are schematic views illustrating various structures of acarbon nanotube:

FIGS. 1A and 1B respectively illustrate schematic longitudinal andtransverse sectional views of an isotropic carbon fiber;

FIGS. 2A and 2B respectively illustrate schematic longitudinal andtransverse sectional views of a carbon nanotube with amorphous carbontherearound;

FIGS. 3A and 3B respectively illustrate schematic longitudinal andtransverse sectional views of a multi-walled nanotube; and

FIGS. 4A and 4B respectively illustrate schematic longitudinal andtransverse sectional views of a single-walled nanotube;

FIG. 5A to 5D cover schematic conceptual views illustratingconfigurations of carbon nanotube devices: FIG. 5A is an example of aconfiguration with a different support, conductive surface layer andwall; FIG. 5B is a configuration in which a support and a layer forminga conductive surface form a single body; FIG. 5C is a configuration inwhich a layer composing a conductive surface and a wall form a singlebody; and FIG. 5D is a configuration in which a support, a layercomprising a conductive surface and a wall form a single body;

FIGS. 6A to 6D covers schematic conceptual views illustratingconfigurations of tunnel junction type carbon nanotube devices: FIG. 6Ais a configuration in which a support, a layer composing a conductivesurface, an insulating layer and a wall are different; FIG. 6B is aconfiguration in which an insulating layer is present on the surface ofa wall; FIG. 6C is a configuration in which an insulating layer ispresent on a part of the surface of a layer composing a conductivesurface; and FIG. 6D is a configuration in which a support, a layercomposing a conductive surface, and a wall form a single body;

FIG. 7 is a schematic view illustrating a carbon nanotube growingapparatus;

FIGS. 8A to 8D are schematic process diagrams illustrating amanufacturing process of an upright type carbon nanotube device usingalumina narrow holes;

FIGS. 9A to 9C are schematic process diagrams illustrating amanufacturing process of an upright type carbon nanotube device using Sinarrow holes;

FIGS. 10A to 10D are schematic process diagrams illustrating amanufacturing process of a tip type carbon nanotube device;

FIG. 11A is a schematic plan view of an embodiment of the tunnel typecarbon nanotube device; and FIG. 11B is a sectional view of the tunneltype carbon nanotube device shown in FIG. 11A cut along the line A-A;

FIG. 12 is a schematic sectional view of another embodiment of thecarbon nanotube device of the invention;

FIG. 13 is a schematic view illustrating a change in anodic oxidizingcurrent when forming Al films on conductive surfaces comprising variousmaterials and causing anodic oxidation of the Al films; and

FIG. 14 is a schematic sectional view of a support provided with a wall,applicable for forming the carbon nanotube device shown in FIG. 5A.

FIG. 15 is a schematic sectional view of an electron-emitting devicewhich is made by using a carbon nanotube device shown in FIG. 8D.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 5A to 5D and FIGS. 6A to 6D are schematic sectional views ofembodiments of the carbon nanotube devices of the present invention. Inthe invention, the term “carbon nanotube” means a structure at leastpartially having a cylindrical structure mainly comprising carbon, inwhich, particularly the cylindrical portion has a diameter of up to 1μm.

Referring to FIGS. 5A to 5D and 6A to 6D, 20 is a support; 21 is a layercomprising a conductive surface of the support 20; 24 is a carbonnanotube conductively binding to the conductive surface 21; 23 is acatalytic super-fine particle present between the carbon nanotube andthe conductive surface 21; and 22 is a wall surrounding the root 24A ofthe carbon nanotube 24 to the conductive surface 21.

The layer comprising the conductive surface 21 of the support is formedon the support 20. The carbon nanotube 24 binds via the catalyticsuper-fine particle 23 to the surface of the layer composing theconductive surface 21. The root 24A of the carbon nanotube 24 where thecarbon nanotube 24 binds to the conductive surface 21 at a binding site,is surrounded by the wall 22.

The support 20 itself has a conductive surface 21, and the carbonnanotube 24 binds via the catalytic super-fine particle 23 to thisconductive surface 21. The root of the carbon nanotube 24 is surroundedby the wall 22. FIG. 5C is an embodiment in which the wall 22 and theconductive surface 21 comprise a semiconductor wall 25, and FIG. 5D isan embodiment in which the support 20 having the conductive surface 21and the wall 22 comprise a semiconductor wall 25.

In the aforementioned example, electrical junction between the carbonnanotube 24 and the conductive surface 21 may be in the form of an ohmicjunction ensuring a sufficient connection, or of a shot-key junction.The junction property varies with the composition of the catalyst andthe layer composing the conductive surface 21 and manufacturingconditions thereof.

FIGS. 6A to 6D illustrate an embodiment in which the carbon nanotube 24conductively binds to the conductive surface 21 by tunnel junction, andthe root is surrounded by the wall 22.

FIG. 6A illustrates an embodiment in which an insulating layer 35 suchas a surface oxide layer is on the layer composing the conductivesurface 21 of the support, the catalytic super-fine particle 23 beingprovided thereon, and the carbon nanotube 24 grows from the catalyticsuper-fine particle 23. FIG. 6B illustrates an embodiment in which aninsulating layer 35 is formed also on the side surface of the wallsurrounding the root 24A of the carbon nanotube 24. FIG. 6C illustratesan embodiment in which an insulating layer 35 is formed on the rootportion of the carbon nanotube 24 where the surface of the layercomposing the conductive surface 21 is exposed. FIG. 6D covers anembodiment in which the support 20, the conductive surface 21 and thewall 22 comprise a semiconductor 25 wall, and an insulating layer 35 isformed on the surface thereof. All these embodiments, indicate a tunneljunction, and the optimum insulating layer thickness depends upon thedriving voltage, the composition and structure of the insulating layer35. The thickness of the insulating layer 35 should preferably be withina range of from a sub-nm to several tens of nm, or more specifically,from 1 to 10 nm. The composition of the insulating layer 35 maycomprise, for example, silicon oxide, titanium oxide, or alumina. Theinsulating layer 35 may be formed, prior to forming the wall 22 on theconductive surface 21, by oxidizing the conductive surface 21, in thecase of FIG. 6A. In the case of the configurations shown in FIGS. 6B and6C, it may be formed, after forming the wall 22, by oxidizing the wall22 and the conductive surface 21 or the conductive surface 21 alone.

FIGS. 5A and 5D and 6A and 6D provide only a few examples. As anotherexample, a configuration shown in FIG. 12 is also within the scope ofthe present invention. In FIG. 12, 91 is an insulating layer formed onthe layer composing a conductive surface 21, and serves also as a wall22 in this embodiment; 53 is a narrow hole formed in the insulatinglayer 91; and 93 is a bridge-shaped path connecting the conductivesurface 21 and the bottom of the narrow hole 53. A catalytic super-fineparticle 23 is provided on the bottom of the narrow hole, and a carbonnanotube 24 is caused to grow vertically to the support surface alongthe wall 91 of the narrow hole 53. The path 93 improves conductivitybetween the catalytic super-fine particle 23 formed on the narrow hole53 bottom and the layer composing the conductive surface 21.

The embodiment shown in FIG. 12 has a configuration in which conductionbetween the carbon nanotube 24 and the conductive surface 21 is ensuredvia the path 93 and the catalytic super-fine particle 23, and the rootof the carbon nanotube 24 to the conductive surface 21 is surrounded bythe wall 22 (i.e., the wall of the narrow hole 53), thus representinganother embodiment of the carbon nanotube device of the invention havinga configuration different from these shown in FIGS. 2 and 3.

For the support 20 in the aforementioned embodiments, when the layer 21giving the conductive surface as illustrated in FIGS. 5A, 6A to 6C and12 is separately provided, there is particular restriction imposed onthe material, and for example, silicon is applicable unless it is freefrom the effect of the forming conditions of the carbon nanotube 24 orthe forming conditions of the wall 22 (including the conditions foranodic oxidation).

In the carbon nanotube device having a configuration shown in FIG. 5B,5C, 5D or 6D, for example, a p-type silicon or a n-type siliconsemiconductor support is suitably applicable.

When considering insulation property required in the form of a deviceand heat resistance upon forming the carbon nanotube 24, the wall 22should preferably comprise a material mainly consisting of alumina orsilicon. The term “a material mainly consisting of silicon” means“containing at least one selected from the group consisting of silicon,silicon oxide and silicon carbide (SiC)”. The wall 22 made of such amaterial has a function of serving to guide the direction of growth ofthe carbon nanotube 24 by forming it so as to surround the root 24A ofthe carbon nanotube 24 to the conductive surface 21. The wall 22surrounding the root 24A of the carbon nanotube 24 to the conductivesurface 21 can be formed, for example, through a generalphotolithographic process or a general patterning process such aselectronic drawing. When preparing a carbon nanotube device having aconfiguration (see FIGS. 8A to 8D) in which the conductive surface 21has carbon nanotubes 24 densely formed thereon that are surrounded bythe walls 22, and the individual roots 24A are isolated by the wall 22layers, silicon or silicon oxide resulting from anodic treatment ofsilicon (Si) or alumina anodic oxidation of aluminum (Al) is suitablyapplicable.

The Al anodic oxidation process is a process of oxidizing the surface ofAl by using Al as an anode and Pt or the like as a cathode in an oxalicacid solution, and impressing a voltage of about 40 V. In this process,narrow holes 53 having a diameter of from several nm to several tens ofnm are obtained on the Al surface, and the surface is simultaneouslyoxidized into alumina.

A carbon nanotube device of the invention can be obtained, for example,by forming an aluminum thin film on a conductive surface 21, thenanodically oxidizing the aluminum thin film, and at this point causingcarbon nanotubes 24 to grow from the conductive surface 21 in narrowholes 53 formed in the Al anodic oxidized film (alumina film). Theconductive surface 21 should preferably comprise a layer containing atleast one element selected from the group consisting of titanium (Ti),zirconium (Zr), niobium (Nb), tantalum (Ta), molybdenum (Mo), copper(Cu) and zinc (Zn), or more preferably, layer comprising Nb. That is,when the conductive surface 21 is formed from such a material, thenarrow holes 53 formed in the alumina film never disappear, and anodicoxidation of Al never peels off the alumina film from the conductivesurface 24. It is also excellent in heat resistance at high temperatureswhen forming the carbon nanotube film to be carried out subsequently.When the conductive surface 21 is formed of such a material, it ispossible to form a bridge-shaped path 93 containing the materialcomposing the conductive surface 21, connecting the narrow hole 53bottom and the conductive surface 21, in the alumina film presentbetween the narrow hole 53 and the layer composing the conductivesurface 21, as shown in FIG. 12, by continuing anodic oxidation evenafter the completion of oxidation of the Al film. Because this path 93can improve conductivity between the narrow hole 53 bottom and theconductive surface 21, it is particularly desirable to compose theconductive surface 21 with the aforementioned material when applying thecarbon nanotube device of the invention to an electron emitting device.

Anodic treatment of Si is carried out by using an Si support as an anodeand platinum as a cathode in a fluoric acid solution and feeding acurrent of several tens of mA/cm². This method makes it possible to forma plurality of narrow holes 53 isolated from each other by silicon orsilicon oxide on the Si support surface, as shown in FIGS. 9A to 9C, forexample. It is therefore possible to obtain a carbon nanotube device ofthe invention by preparing a conductive silicon support (p-type Si orthe like) as a support 20, anodizing the surface of the conductivesilicon support 20 to form narrow holes 53 isolated by silicon orsilicon oxide, and causing carbon nanotubes 24 to grow from the bottomof the narrow holes 53.

When forming a carbon nanotube 24 in the narrow hole 53 resultant fromAl anodic oxidation or anodization of Si as described above, it isrecommendable to form a catalytic super-fine particle 23 on the narrowhole 53 bottom, i.e., on the conductive surface 21, and to cause thecarbon nanotube 24 to grow from the surface of this catalytic super-fineparticle 23. Applicable catalyst materials include, for example, iron(Fe), cobalt (co) and nickel (Ni).

The catalytic super-fine particle 23 should preferably have a particlediameter within a range of from 1 to 10 nm, or more preferably, from 2to 50 nm. A catalyst of such a material having such a size canefficiently cause a carbon nanotube 24 to grow and achieve a sizeexcellent in electron emitting efficiency.

For depositing such a catalytic super-fine particle 23 into the narrowhole 53, for example, the AC electro-deposition process is effectivelyapplicable.

When preparing a Co super-fine particle, for example, it suffices toimpress an AC (50 Hz) voltage of about 15 V to a space between theconductive surface 21 and the opposed electrode in an aqueous solutionof CoSO₄.7H₂O=5% and H₃BO₃=2%. This method permits introduction of thecatalytic super-fine particle 23 even into the slightest narrow hole 53formed by, for example, the Al anodic oxidation.

Another method for introducing the catalytic super-fine particle 23 intothe narrow hole 53 comprises vapor-depositing Fe, Co or Ni onto theconductive surface 21 having a narrow hole 53 and a wall 22, andthermally aggregating this vapor-deposited film.

An effective method for causing a carbon nanotube 24 to grow on theconductive surface 21 surrounded by the thus formed carrier, or on theconductive surface 21 surrounded by the wall 22 and provided with thecatalyst comprises, for example, thermally treating the support 20 in agas atmosphere containing not only the raw material gas, but also addedwith a diluent gas or a growth accelerator gas. Many gases containingcarbon are applicable as a raw material gas.

Examples of the raw material gas include gases comprising only carbonand hydrogen, such as methane, ethane, propane, butane, pentane, hexane,ethylene, acetylene, benzene, toluene and cyclohexane, and gasescomprising carbon, hydrogen and other elements, such as benzonitrile,acetone, ethyl alcohol, methyl alcohol and carbon monoxide.

Preferable raw materials from among these applicable ones, somewhatvarying with the kind of the support 20, the composition of the growthnucleus, growing temperature and pressure, are ones comprising carbon,hydrogen and oxygen, which make it difficult for impurities to come in.

In view of the low temperature growth of the carbon nanotube 24,ethylene, acetylene and carbon monoxide are preferable. Hydrogen ispreferable as a growing or growth accelerating gas. However, becauseeffectiveness of hydrogen depends upon the raw material gas, thereaction temperature, and the composition of the growth nucleus,hydrogen is not an essential requirement.

A diluent gas is effective when growth rate is too high, or whenalleviating toxicity or explosivity of the raw material gas, andapplicable diluent gases include inert gases such as argon and heliumand nitrogen.

The manufacturing method of an embodiment of the carbon nanotube deviceof the invention shown in FIGS. 8A to 8D will now be described indetail.

First, as shown in FIG. 8A, a film mainly comprising Ti, Zr, Nb, Ta, Mo,Cu or Zn is formed on an Si wafer support, and then an Al film is formedwithout exposure to the air. This film forming method is typicallyrepresented by the sputtering process based on a sputtering apparatushaving multiple targets.

Then, the support 20 is immersed in a 0.3 M oxalic acid solution foranodic oxidation of Al, and a voltage of 40V is impressed with thesupport 20 as an anode and a Pt as a cathode while keeping a temperatureof 17° C. As a result, as shown in FIG. 13, the Al surface is firstoxidized, leading to a decrease in current value which however increasesalong with formation of narrow holes 53 resulting from oxidation of theAl film, and shows a constant value. Upon the completion of oxidation ofthe Al film thereafter, the current value caries with the materialcomposing the conductive surface 21. For example, the layer composingthe conductive surface 21 comprises Ti, Zr, Nb, Ta or Mo, the anodicoxidizing current exhibit a decrease as shown in curve (a) on FIG. 13.When the layer composing the conductive surface 21 is formed with Cu orZn, on the other hand, the anodic oxidizing current shows once anincrease and then a decrease as shown in curve (b) on FIG. 13. It ispossible to manufacture a structure for a carbon nanotube device shownin any of FIGS. 5A to 5D, 6A to 6D, FIGS. 12 and 14 through selection ofa material for the conductive surface 21 and control of timing forstoppage of anodic oxidation.

When forming the conductive surface 21 with Ti, Zr, Nb, Ta or Mo, andanodic oxidation of the Al film formed on the conductive surface 21 isdiscontinued immediately prior to a decrease in the anodic oxidizingcurrent curve, for example, the Al layer formed on the conductivesurface totally oxidized in the thickness direction into alumina asshown in FIG. 8B. The narrow hole 53 has not as yet reached theconductive surface 21, and there is available a structure in whichalumina is present with a thickness of from about 1 to 10 nm between thebottom of the narrow hole 53 and the conductive surface 21. Thisstructure is applicable as a structure for a carbon nanotube device inwhich the wall 22 and the insulating layer 35 are made of the samematerial in the carbon nanotube device, shown in FIG. 6B, in which theconductivity between the carbon nanotube 24 and the conductive surface21 tunnel effect.

When composing the conductive surface with Ti, Zr, Nb, Ta or Mo, andanodic oxidation of the Al film formed on the conductive surface 21 isdiscontinued after start of a decrease in the anodic oxidizing currentcurve, it is possible to form a path 93 between the conductive surface21 and the bottom of the narrow hole 53 as shown in FIG. 12. This path93 is known, as a result of a material analysis, to contain the materialcomposing the conductive surface 21, i.e., Ti, Zr, Nb, Ta or Mo andoxygen, and formation of this path permits considerable improvement ofconductivity between the conductive surface 21 and the narrow hole 53.This further leads to improvement of depositing efficiency of acatalytic super-fine particle 23 to the narrow hole 53, and remarkableimprovement of conductivity between the conductive surface 21 and acarbon nanotube 24 upon formation of the carbon nanotube 24 in thenarrow hole 53. Although the reason of formation of the path is notclear, alumina solution into the electrolyte occurs on the bottom of thenarrow hole 53 in the process of formation of the narrow hole 53 throughanodic oxidation of the Al film, and a phenomenon is observed in whichAl ions are drawn through the Al portion anodically oxidized by theelectric field into the electrolyte along with oxidation of Al at theinterface of anodic oxidation (interface between alumina and Al). It isconsiderable, from this observation, that, when continuing anodicoxidation even after the completion of anodic oxidation of the Al film,anodic oxidation reaches the conductive surface 21, and serves to drawout the material composing the conductive surface 21 (for example, Ti,Zr, Nb, Ta or Mo) through the alumina layer on the bottom of the narrowhole 53 into the electrolyte. Because the oxide of Ti, Zr, Nb, Ta or Mois chemically stable and is not easily dissolved into the electrolyte,it is considered that alumina remains in the form of the path 93 on thebottom of the narrow hole 53.

When annealing the structure having the path 93 formed therein in ahydrogen gas, inert gas, or hydrogen and inert gas atmosphere,conductivity between the conductive surface 21 of the structure and thenarrow hole 53 can further be improved. The reason of improvement ofconductivity between the conductive surface 21 of the structure and thenarrow hole 53 by annealing in not as yet clear, but is consideredattributable to the reduction of the path 93.

The further improvement of conductivity between the conductive surface21 of the structure and the narrow hole 53 in turn improves depositionefficiency of the catalytic super-fine particle 23 onto the bottom ofthe narrow hole 53, and further improves conductivity between theconductive surface 21 and a carbon nanotube 24 after forming the carbonnanotube 24 in the narrow hole 53. This is therefore a process which ispreferable particularly when applying the carbon nanotube device of theinvention to an electron emitting device. Annealing should preferably becarried out at a temperature within a range of from 200 to 1,100° C. fora period of time within a range of from 5 to 60 minutes.

When the conductive surface 21 comprises Cu or Zn, and anodic oxidationis discontinued after start of decrease in anodic oxidizing current, astructure having a narrow hole 53 reaching the conductive surface 21 isavailable as shown in FIG. 11. This structure is applicable as astructure for a carbon nanotube device in which the carbon nanotube 24binds directly to the exposed conductive surface 21 as shown in FIG. 5A.

In the aforementioned structures in the above embodiments, the diameterof the narrow hole 53 can be enlarged by immersing the structure into aphosphoric acid solution of about 5 wt.%.

A carbon nanotube device as shown in FIGS. 5A to 5D, 6A to 6D or 12 isavailable by depositing the catalytic super-fine particle 23 into thenarrow hole 53 by the use of the aforementioned method, and causing acarbon nanotube 24 to grow from the surface of the deposited catalyticsuper-fine particle 23.

Growth of a carbon nanotube 24 can be accomplished by the use of, forexample, a reactor as shown in FIG. 7. This will now be described withreference to FIG. 7.

In FIG. 7, 41 is a reactor; 42 is a support; 43 is an infrared-rayabsorbing plate, serving also as a support holder; 44 is a tube forintroducing a raw material gas such as ethylene, and should preferablybe arranged so as to achieve a uniform raw material gas concentrationnear the support 42; 45 is a tube for introducing a reactionaccelerating gas such as hydrogen or a diluent gas such as helium; andthe raw material gas tube 44 is arranged near an infrared-raytransmitting window 49 so as to serve to prevent the window 49 frombeing dim with decomposition of the raw material gas.

Also in FIG. 7, is a gas exhaust line 46 which is connected to a turbomolecular pump or a rotary pump (not shown); 47 is an infrared lump forheating the support; and 48 is a condensing mirror for collectingefficiently infrared rays for absorption. Although not shown, a vacuumgauge for monitoring pressure within the container; a thermocouple formeasuring temperature of the support 42 and the like are provided.

The apparatus is not of course limited to those described here. Anelectric furnace type apparatus heating the entire assembly from outsidemay well be employed. In actual growth of a carbon nanotube 24, stepscomprise, for example, introducing ethylene as a raw material gas in anamount of 10 sccm from the raw material gas tube 44 into the apparatus,introducing 10 sccm hydrogen as the growth accelerating/diluent gas fromthe reaction accelerating gas tube 45; applying a pressure of 1000 Pa inthe reactor, heating the support 42 by an infrared-ray lamp to 700° C.and causing a reaction for 60 minutes.

The diameter of the thus synthesized carbon nanotube 24, depending uponthe diameter of the catalytic super-fine particle 23 and other reactionconditions, is within a range of from several nm to a submicron size andthe length is within a range of from several tens of nm to several tensof μm. Since a terminus of the carbon nanotube 24 already bindsconductively to the conductive surface, the carbon nanotube device ofthe invention is favorable particularly in such applications as electricfield electron emission, a probe such as STM, a quantum device, avibrator for a micromachine, and various electrodes.

Because carbon is chemically stable and has a high strength, theinvention is applicable also for the purposes of improving the support42 surface.

As shown in FIG. 15, by locating a counter electrode 1501 at a positionopposite to the conductive surface 21 of the carbon nanotube device ofthe present invention, for example, shown in FIG. 8D, anelectron-emitting device can be obtained. The electron-emitting devicein FIG. 15 is constructed in such a manner that a potential can beimpressed between the electrode 1501 and the conductive surface 21.

The present invention will now be described further in detail by meansof examples.

Example 1

(1) An Si wafer support having a clean surface was provided as asupport. Ti was formed into a film having a thickness of 100 nm on thesurface of the Si wafer by the sputtering process. The sputtering wascarried out by applying RF power of 400 W and under Ar gas partialpressure of 5 mm Torr. After forming the Ti film, an Al film having athickness of 1 μm was formed under the same conditions except forchanging the target to Al in the same apparatus, thereby preparing asupport 20 as shown in FIG. 8A.

A support having the layered structure as shown in FIG. 8A was preparedin the same manner as above except that the Ti thin film was changed toa Zr, Nb, Ta, Mo, Cu, Zn, Pd or Au thin film.

Each of the resultant supports was immersed in a 0.3 M oxalic acidsolution, and then anodic oxidation of Al was carried out by using thesupport as an anode and Pt as a cathode and applying a voltage of 40 Vwhile keeping a temperature of 17° C. As shown in FIG. 13, the beginningof the anodic oxidation, anodic oxidizing current decreased due to rapidoxidation of the Al surface. Toward the start of formation of a narrowhole 53 along with oxidation of the Al film, the current showedsubstantially a constant value. Thereafter, for each support having aconductive surface 21 comprising a Ti film, a Zr film, an Nb film, a Tafilm, or an Mo film, anodic oxidation was discontinued after a rapiddecrease in current value as shown by a curve (a) in FIG. 13. The periodwas for about ten minutes. These supports shall hereinafter be calledGroup (1) supports.

For each support in which the conductive surface comprised a Cu film ora Zn film, anodic oxidation was discontinued upon decrease after oneincrease in current value as shown by a curve (b) in FIG. 13. The periodwas for about ten minutes. These supports shall hereinafter be calledGroup (2) supports.

For each support in which the conductive surface comprised a Pd film oran Au film, anodic oxidation was discontinued after a sharp increase incurrent value as shown by a curve (c) in FIG. 13. The period was forabout ten minutes. These supports shall hereinafter be called Group (3)supports.

For these Groups (1) to (3) supports as described above, structures wereanalyzed by means of a transmission type electron microscope: in Group(1) supports, the aluminum film on the conductive surface was completelyoxidized in the thickness direction as shown in FIG. 12, and the narrowhole 53 did not reach the conductive surface. It was confirmed that abridge-shaped path 93 containing a metal (for example, Ti, Zr, Nb, Ta orMo) composing the conductive surface was formed between the conductivesurface and the bottom of the narrow hole.

For Group (2) supports, it was confirmed that the Al film on theconductive surface was fully oxidized in the thickness direction, andthe narrow hole reached the conductive surface as shown in FIG. 5A. ForGroup (3) supports, although the Al film on the conductive surface wasoxidized, the narrow holes had disappeared. The reason of disappearanceof the narrow holes is not clear, but it is considered attributable tothe fact that a reaction between the conductive surface and theelectrolyte produced a large electric current, and oxygen gas producedalong with this destroyed the narrow holes.

(2) Layers as shown in FIG. 8A having a Ti film, a Zr film, an Nb film,a Ta film or an Mo film formed on the Si wafer support surface wereprepared in the same manner as in (1) above. Each of these supports wasimmersed in a 0.3 M oxalic acid solution, and anodic oxidation of Al wascarried out by using the support as an anode and Pt as a cathode andapplying a voltage of 40 V while keeping a temperature of 17° C. Anodicoxidation was discontinued immediately before observing a decrease inanodic oxidizing current as represented by curve (a) in FIG. 13. Theperiod was for about eight minutes. These supports shall hereinafter becalled Group (4) supports. The structure was analyzed for Group (4)supports by the use of a transmission type electron microscope. Thealuminum film on the conductive surface was completely oxidized in thethickness direction, and the narrow hole 53 did not reach the conductivesurface as in Group (1) supports. The path observed in Group (1)supports was not observed.

Then, easiness of plating onto the narrow hole surface was measured bythe following method for Group (1) and Group (4) supports. The stepscomprised immersing each of Group (1) and Group (4) supports in anaqueous solution containing 5 wt. CoSO₄.7H₂O, and 2 wt. % H₃BO₃,applying a potential between opposed Co electrodes, and measuring thepotential necessary for plating Co particles on the narrow hole bottomas a support potential corresponding to a calomel standard electrode.The resultant potential value was within a range of from about −1 to−1.5 V for Group (1) supports, whereas a potential of at least −10 V wasrequired for Group (4) supports. This suggests that the bridge-shapedpath 93 formed in Group (1) supports played an important role forimprovement of conductivity between the bottom of the narrow hole andthe conductive surface.

(3) Group (1), (2) and (4) supports were prepared in the same manner asdescribed under (1) and (2) above.

Then, a catalytic super-fine particle 23 was prepared by the ACelectro-deposition process on the bottom of the narrow hole for eachsupport. The support having narrow holes thus prepared was immersed inan aqueous solution containing 5% CoSO₄.7H₂O and 2% H₃BO₃, and astructure having Co super-fine particles on the bottom of the narrowholes as shown in FIG. 8C was obtained by impressing an AC (50 Hz)voltage of 15 V for few seconds.

Then, a carbon nanotube was grown in a reactor as shown in FIG. 7.First, the support having the catalytic super-fine particles was placedin the reactor, then hydrogen in an amount of 10 sccm was introducedfrom a reaction accelerating gas tube 45 and a pressure of 500 Pa waskept in the reactor. The support temperature was brought to between 400and 800° C. by turning on an infrared lamp.

After temperature stabilization, a raw material gas such as methane,ethylene, acetylene, carbon monoxide or benzene was introduced in anamount of 10 sccm from a raw material gas tube 44, and the pressure inthe reactor of 1000 Pa was kept for 20 minutes. Then, the infrared lampwas turned off to interrupt the supply of gas, and the support was takenout into the open air after bringing the support temperature to the roomtemperature.

The support thus taken out was observed by means of an FE-SEM (FieldEmission-Scanning Electron Microscope). In all the observed supports,carbon nanotubes had grown from the catalytic super-fine particles onthe bottom of the narrow holes as shown in FIG. 8D. The carbon nanotubehad a diameter within a range of from several nm to several tens of nm,depending upon the raw material gas and the catalytic super-fineparticle, and had grown in the vertical direction along the narrow holefrom the support with a terminus of the carbon nanotube 24 binding tothe support.

When methane was used as a source gas, however, growth of the carbonnanotube was less remarkable. With a source gas of benzene, there werefluctuations in diameter among carbon nanotubes: the largest diameterwas almost the same as that of the narrow hole. The optimum growthtemperature of the carbon nanotube was higher in the order of carbonmonoxide, acetylene, ethylene, benzene and then methane.

For the purpose of evaluating properties of the resultant carbonnanotube devices, each of the carbon nanotube devices of Groups (1), (2)and (4) was placed in a vacuum chamber, and an opposite electrode wasarranged at a distance of 0.1 mm from the support in parallel therewithso that the carbon nanotube forming surface of the support faced theelectrode. After evacuating the chamber to 10⁻⁸ Torr, a positive voltagewas impressed to the opposite electrode, and the quantity of electronsemitted from the carbon nanotube was measured. As a comparative example,three kinds of supports having a conductive surface were prepared byusing the same materials as those of Group (1), (2) and (4) supportsrespectively. Then ethanol dispersing carbon nanotubes was coated on therespective conductive surfaces of the supports. The amount of the carbonnanotube coated on the surface was almost the same as those of the Group(1), (2) and (4) carbon nanotube devices each of which was prepared byusing ethylene as a raw material gas. Subsequently, the quantity ofelectrons emitted form the respective supports provided with the carbonnanotube coatings was measured in the same manner as the Group (1), (2)and (4) carbon nanotube devices.

As a result, as to Groups (1), (2) and (4) carbon nanotube devices,emitted current was observed starting from impression of about 100V, andthe amount of current upon impressing 200V, was ten times larger thanthat available from a film in which carbon nanotubes were simplydispersed.

This is attributable to the fact that the carbon nanotubes weresufficiently connected to the electrode and the isolated carbonnanotubes extended in the vertical direction. These results permittedconfirmation that the device of the invention had an excellent functionas an electron emitting source.

Among Group (1), (2) and (4) carbon nanotube devices, the quantity ofemitted electrons was larger in the order of Group (2), Group (1) andthe Group (4).

(4) Group (1) support was prepared in the same manner as described under(1) above. After heat-treating the support in a mixed gas of H₂:He=2.98(volume ratio) at 500° C. for an hour, a carbon nanotube device wasprepared in the same manner as in (3) above. By the use of this carbonnanotube device, the quantity of emitted electrons was measured in thesame manner as in (3) above. As a result, a quantity of emittedelectrons even superior to that of the carbon nanotube device preparedby the use of Group (1) support, as measured in (3) above, wasconfirmed. The reason why the carbon nanotube device prepared by the useof a heat-treated support gives such an effect is not clear. As aresult, however, of the improvement of conductivity of the path broughtabout by the reduction of the path in the heat treatment, the depositingefficiency of the catalytic super-fine particles onto the narrow holesis considered to be improved, and this further improves conductivitybetween the conductive surface and the carbon nanotube.

Example 2

An example of the manufacturing method when the catalytic metal and theelectrode film are the same will now be described.

As in Example 1, by the use of an Si wafer substrate cleaned as asupport, a Co film having a thickness of 0.1 μm was formed on thesupport by the RF sputtering process. Then, in the same apparatus withthe target changed to Al, and Al film was continuously formed into athickness of 0.2 μm to form an Al/Co layered film. The sputteringconditions included an RF power of 400 W and an Ar atmosphere at 5mTorr.

This support was immersed in a 0.3 M oxalic acid solution, and the Alfilm was anodically oxidized by using support as an anode and Pt as acathode and impressing 40 V while keeping a temperature of 17° C. As aresult of voltage impression, the Al surface was first rapidly oxidized,leading to a decrease in current value. After start of formation ofnarrow holes, the current value increased to a constant value. Upon thecompletion of oxidation of the Al film, the narrow hole reached theundercoat Co layer and the current value gradually increased. Anodicoxidation was therefore discontinued at this point. The period was forabout two minutes.

To widen the bore of the narrow holes, the support was immersed in aphosphoric acid solution of about 5 wt. % for 40 minutes and taken out.A support provided with an alumina film, having narrow holes of adiameter of about 50 nm on the surface was obtained. As a result of thistreatment, the undercoat Co surface was exposed on the bottom of thenarrow holes and could be used as a catalyst portion.

Then, the support was place in a reactor as shown in FIG. 7, andhydrogen gas was introduced in an amount of 20 sccm from the reactionaccelerating gas tube 45 to bring the pressure in the reactor to 500 Pa.The support temperature was increased to 600° C. by turning on aninfrared lamp.

After stabilization of temperature, use the raw material gas ethylenediluted with nitrogen to 10% was introduced in an amount of 20 sccm tobring pressure in the reactor to 1,000 Pa which was kept for 20 minutes.Thereafter, the infrared lamp was turned off to interrupt the supply ofgas, and then, the support temperature was brought back to the roomtemperature. The support was then taken out into the open air.

The surface of the resultant support was observed by means of an FE-SEM:carbon nanotubes had grown from the narrow hole portion, but the carbonnanotubes had a large diameter of several 10 nm, and there were observedmany portions of the narrow holes where the growth did not occur. Thissuggests that the catalyst present in the narrow holes should preferablybe in the form of super-fine particles as in Example 1.

For the purpose of evaluating properties of the resultant carbonnanotube device, the Co film of the support attached with an electrodewas placed in a vacuum chamber as in Example 1, and an oppositeelectrode was arranged at a distance of 0.1 mm from the support inparallel therewith. After evacuating the chamber to 10⁻⁸ Torr, apositive voltage was impressed to the opposite electrode, and thequantity of electrons emitted from the carbon nanotubes was measured.

As a result, emitted current was observed starting from impression ofabout 150 V, and the amount of current upon impressing 200 V, which wasabout a half that in Example 1, was several times as large as thatavailable from a film in which carbon nanotubes were simply dispersed.This permits formation that the device of the invention has a sufficientfunction as an electron emitting source.

The amount of emitted current is smaller than that available from theelectron emitting device prepared by the use of the carbon nanotubes ofExample 1. This is considered attributable to the fact that, althoughthe carbon nanotubes are sufficiently connected to the electrode, thediameter of the nanotube is somewhat large, resulting in insufficientconcentration of electric field and a low growth density of the carbonnanotube.

Example 3

An example of carbon nanotube device in which the wall, the layercomposing the conductive surface and the support are all prepared withSi will now be described with reference to the schematic processdescriptive view shown in FIGS. 9A to 9C and the equipment schematicdiagram shown in FIG. 7.

An ohmic contact was prepared by using a p-type substrate having a lowresistance (several mm to several hundred mmΩcm) as a support, formingan Al film having a thickness of about 1 μm on the back of the p-type Sisubstrate and annealing at 400° C.

Then, anodization of the support was carried out with the supportimmersed in an aqueous solution containing 10% fluoric acid and 5%alcohol to serve as an anode and with Pt as a cathode. Al on the backwas arranged so as not to come into contact with the fluoric acidsolution, and an electrode was taken from the Al surface. Conditionswere set to give a current value of several tens of mA/cm² uponanodization. After the completion of anodization, the support was takenout, and washed with distilled water and IPA. As a result of thisprocess, narrow holes of several nm to several tens of nm as shown inFIG. 9A were formed on the Si surface, and the individual narrow holeswere isolated from each other by p-type Si walls 22.

The support was placed in a vacuum depositing unit and evacuation wascarried out up to a degree of vacuum of 10⁻⁶ Torr, and Fe wasvapor-deposited into a thickness of 0.3 nm on the upper surface by theresistance heating vapor depositing process. Thermal aggregation of thevapor-deposited film was accomplished by heating the support to 700° C.while keeping a vacuum. This resulted in a structure in which catalyticsuper-fine particles were placed in the narrow holes as shown in FIG.9B.

Then, the support was placed in the reactor shown in FIG. 7. First,hydrogen gas was introduced in an amount of 20 sccm from the reactionaccelerating gas tube 45 to keep a pressure of 500 Pa in the reactor.The support temperature was increased to 650° C. by turning on aninfrared lamp. After stabilization of temperature, ethylene wasintroduced in an amount of 20 sccm to bring the pressure in the reactorto 2,000 Pa, which was kept for 20 minutes. Thereafter, the infraredlamp was turned off to cut the supply of the gas. Then, after bringingthe support temperature to the room temperature, the support was takenout into the open air, thereby obtaining a carbon nanotube device.

Another carbon nanotube device was prepared in the same manner as aboveexcept that Co, Ni or Pd was used as a material for the catalyticsuper-fine particles.

The surfaces of these four kinds of carbon nanotube devices wereobserved by means of an FE-SEM. For the devices using Fe, Co and Ni ascatalysts, while growth of the carbon nanotubes from the narrow holeportion was observed, almost no growth of the carbon nanotubes in thenarrow holes was observed for the device using Pd.

For the purpose of evaluating properties of the resultant carbonnanotube devices prepared by the use of Fe, Co or Ni as a catalyst, thesupport attached with an electrode was placed in a vacuum chamber, andan opposite electrode was arranged at a distance of 0.1 mm from thesupport in parallel therewith, as in Example 1. After evacuating thechamber to 10⁻⁸ Torr, a positive voltage was impressed to the oppositeelectrode, and the quantity of electrons emitted from the carbonnanotube was measured.

As a result, the electron emission was observed, starting fromimpression of about 100 V, and the amount of current upon impressing 200V was about ten times as large as that of a film in which carbonnanotubes were simply dispersed.

This is attributable to the fact that the carbon nanotubes weresufficiently connected to the electrode and the isolated carbonnanotubes extended in the vertical direction from the support. Thispermitted confirmation that the device of this example had an excellentfunction as an electron emitting source.

Example 4

A configuration of a tip type carbon nanotube device and a typicalmanufacturing method thereof will now be described with reference to theprocess schematic descriptive views shown in FIGS. 10A to 10D and theequipment schematic diagram shown in FIG. 7.

A resist 71 (AZ manufactured by Hext Company) was coated into athickness of 0.5 to 1 μm by means of a spinner as shown in FIG. 10A on alow-resistance Si wafer serving as a support. After UV exposure with theuse of a mask, the exposed portion was peeled off with an organicsolvent, and a submicron (0.1 to 1 μm) hole was pierced on the resist. Ahole 72 was prepared also in the Si wafer by introducing the supportinto a plasma etching unit, and etching the Si wafer from the holeportion of the resist. The etching conditions included SF₄ gas of 5 Pa,an RF power of 150 W, and a treating period of a minute. Then, thesupport was placed in a resistance heating vapor depositing unit and aCo—Ni alloy (composing ratio: 1:1) film was formed into a thickness of 1nm on the resist layer surface and the hole surface of the Si wafer.Then, the resist was lifted off, and thermal aggregation of the Co—Nithin film was caused by annealing it in vacuum at 500° C. to convert itinto a catalytic super-fine particle 73.

Then, the support was placed in the reactor shown in FIG. 7. First,hydrogen gas was introduced in an amount of 20 sccm from the reactionaccelerating gas tube 45 to keep a pressure of 500 Pa in the reactor.The support temperature was increased to 700° C. by turning on aninfrared lamp. After stabilization of temperature, acetylene gas dilutedwith nitrogen (90%) was introduced in an amount of 20 sccm to bring thepressure in the reactor to 3,000 Pa, which was kept for 20 minutes.Thereafter, the infrared lamp was turned off to discontinue the supplyof the gas. Then, after bringing the support temperature to the roomtemperature, the support was taken out into the open air.

The surface of the resultant support was observed with an FE-SEM. Acarbon nanotube had grown from the catalytic super-fine particle 73portion in the hole 72 as shown in FIG. 10D, having a diameter within arange of from several nm to several tens of nm.

For the purpose of evaluating properties of the resultant carbonnanotube device, the support was attached to the probe portion of theSTM/AFM evaluating unit to form a probe connected to an electrode. As aresult of the STM/AFM evaluation, a satisfactory image based on a carbonnanotube tip was obtained. This is considered to be due to a gooddirectivity of the carbon nanotube surrounded by the wall, sufficientelectrical connection between the carbon nanotube and the electrode (thelow-resistance Si in this example), and the sharp tip thereof.

Example 5

A typical configuration of a tunnel type carbon nanotube device will nowbe described with reference to the schematic diagrams shown in FIGS. 11Aand 11B.

First, an alumina film 22 provided with electrodes 81 and 82 and a finehole adjacent to the electrode 81 was formed as shown in FIG. 11A on ahigh-resistance or an insulating support 80.

A catalytic super-fine particle was introduced into the narrow hole. Acarbon nanotube 24 had grown from the surface of the catalyticsuper-fine particle and reached the top of the electrode 82. A thininsulating layer was provided on a part of the electrode 82, and wasconnected to the carbon nanotube 24 thereabove via the insulating layer87. An insulating coat film was provided over the insulating layer 87and a wall 86. The electrode 81 and the carbon nanotube were isolatedfrom each other by the wall. The electrodes 81 and 82 were connected inthe sequence of the electrode 81—the wall alumina layer 22—the catalyticsuper-fine particle 23—the carbon nanotube 24—the insulating layer87—the electrode 82.

Current-voltage property of the resultant device having theaforementioned configuration was evaluated after connection of theelectrodes by inserting it into liquid helium and cooling it to 4 K. Anegative-resistance area was observed as a result in the current-voltageproperty. This is considered to be a result of a resonance tunnel effectbecause the device of the invention has double barriers. By theutilization of this phenomenon, the device of the invention is expectedto be applied for high-frequency detection and oscillation.

When manufacturing carbon nanotubes by the pyrolysis process by simplyseeding catalytic super-fine particles at a high density on a flatsurface, there is a high probability that a single carbon nanotube growswhile causing connection of many catalytic super-fine particles in andoutside. More specifically, directivity of a carbon nanotube connectinga plurality of catalytic super-fine particles as above is not uniformand the geometry including diameter cannot be uniform in many cases. Itis therefore desirable to cause individually isolated catalyticsuper-fine particles to grow.

While a carbon nanotube is often applied as an electrode, it is thegeneral practice on the present level of art, after synthesis of thecarbon nanotubes, to attach the carbon nanotubes to the substrate byconducting paste scatter them onto the substrate and form a metal filmon them.

The carbon nanotube device of the invention has a feature in that it hasa configuration in which the carbon nanotube conductively binds to theconductive surface without the need to conduct such electrode attachmentafter synthesis. The device having such a configuration can be preparedby selecting an optimum combination of a composition and a shape of theconductive surface, the catalytic super-fine particle, and the barrierisolating the super-fine particles, and a synthesizing method of carbonnanotube as described in this specification. According to the presentinvention, there are available, for example, the following advantages:

(1) There is available a satisfactory device electrically connected toelectrodes and in which carbon nanotube are isolated from each other.

(2) An electron emitting device excellent in electron emitting propertycan be obtained.

(3) There is available a probe such as an STM or an AFM giving asatisfactory image and having a high strength.

(4) A novel tunnel type device using carbon nanotube is available.

(5) The carbon nanotube device of the invention has a configuration inwhich the conductive surface comprises a layer containing Ti, Zr, Nb,Ta, Mo, Cu or Zn, or particularly a layer containing Nb, and an Alanodic oxidation film, i.e., an alumina film having a fine hole isprovided on the surface film of the conductive surface. In thisconfiguration, the alumina film and the conductive surface show asatisfactory adherence, so that the alumina film never peels off theconductive surface at the interface. This configuration is thereforefavorable for carbon nanotube applicable for a high-quality electronemitting device or a probe for STM or AFM.

(6) When a semiconductor such as a p-type Si is used as a support, it ispossible to easily form a plurality of narrow holes isolated by a wallof Si or Si oxide on the surface of the p-type Si by anodizing thesurface of the p-type Si. By causing carbon nanotubes to grow from thesenarrow holes, the growing direction of the carbon nanotube is regulatedby the wall. It is therefore possible to form a carbon nanotube devicehaving carbon nanotubes having substantially a uniform directivity at alow cost.

(7) When connecting the conductive surface and the carbon nanotubes toelectrodes via the catalytic super-fine particles, it is desirable forgrowth control of carbon nanotubes to select one or more metals from Fe,Co and Ni for the catalytic super-fine particles.

(8) The carbon nanotube device in which the carbon nanotubes and theconductive surface are in an electrical tunnel junction is preferablewhen manufacturing a resonance tunnel device or the like.

While the present invention has been described with respect to what ispresently considered to be the preferred embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments. The present invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. An electronic device comprising: (i) a first electrode and a secondelectrode, which are disposed on a surface of a substrate; and (ii) aplurality of carbon nanotubes, wherein each of the carbon nanotubes iselectrically connected to the first electrode and the second electrodeand is at a distance from the surface of the substrate.
 2. A method ofmanufacturing an electronic device, the method comprising: (i) preparinga first electrode and a second electrode on a surface of a substrate;and (ii) preparing a plurality of carbon nanotubes, such that each ofthe carbon nanotubes is electrically connected to the first electrodeand the second electrode and is at a distance from the surface of thesubstrate.
 3. The electronic device according to claim 1, wherein eachof the carbon nanotubes is formed on the first electrode or the secondelectrode by a CVD method using a catalyst.
 4. The method according toclaim 2, wherein each of the carbon nanotubes is formed on the firstelectrode or the second electrode by a CVD method using a catalyst. 5.An electronic device comprising: (i) a plurality of carbon nanotubesprovided on a surface of a substrate, each of the carbon nanotubeshaving a first end portion and a second end portion; and (ii) a firstconductive member and a second conductive member, wherein the first endportion of each of the carbon nanotubes is positioned between a part ofthe first conductive member and the surface of the substrate and iselectrically connected to the first conductive member, and wherein thesecond end portion of each of the carbon nanotubes is positioned betweena part of the second conductive member and the surface of the substrateand is electrically connected to the second conductive member.
 6. Theelectronic device according to claim 5, wherein each of the carbonnanotubes is formed on the first electrode or the second electrode by aCVD method using a catalyst.
 7. The electronic device according to claim5, wherein each of the carbon nanotubes is at a distance from thesurface of the substrate.
 8. An electronic device comprising: (i) afirst electrode and a second electrode, which are disposed on a surfaceof a substrate; and (ii) a plurality of carbon nanotubes, wherein eachof the carbon nanotubes is electrically connected to the first electrodeand the second electrode and is formed on the first or second electrodeby a CVD method using a catalyst.
 9. A method of manufacturing anelectronic device, the method comprising: (i) preparing a firstelectrode and a second electrode on a surface of a substrate; and (ii)preparing a plurality of carbon nanotubes, such that each of the carbonnanotubes is electrically connected to the first electrode and thesecond electrode, and wherein each of the carbon nanotubes is formed onthe first or second electrode by a CVD method using a catalyst.